r65262 | neal.norwitz | 2008-07-28 07:22:45 +0200 (Mon, 28 Jul 2008) | 11 lines

Backport r65182.  This change modified from using the unsigned max value
to the signed max value similar to 2.5 and trunk.

Issue #2620: Overflow checking when allocating or reallocating memory
was not always being done properly in some python types and extension
modules.  PyMem_MALLOC, PyMem_REALLOC, PyMem_NEW and PyMem_RESIZE have
all been updated to perform better checks and places in the code that
would previously leak memory on the error path when such an allocation
failed have been fixed.


Index: Python-2.4.4/Include/pymem.h
===================================================================
--- Python-2.4.4.orig/Include/pymem.h
+++ Python-2.4.4/Include/pymem.h
@@ -66,8 +66,12 @@ PyAPI_FUNC(void) PyMem_Free(void *);
    for malloc(0), which would be treated as an error. Some platforms
    would return a pointer with no memory behind it, which would break
    pymalloc. To solve these problems, allocate an extra byte. */
-#define PyMem_MALLOC(n)         malloc((n) ? (n) : 1)
-#define PyMem_REALLOC(p, n)     realloc((p), (n) ? (n) : 1)
+/* Returns NULL to indicate error if a negative size or size larger than
+   Py_ssize_t can represent is supplied.  Helps prevents security holes. */
+#define PyMem_MALLOC(n)		(((n) < 0 || (n) > INT_MAX) ? NULL \
+				: malloc((n) ? (n) : 1))
+#define PyMem_REALLOC(p, n)	(((n) < 0 || (n) > INT_MAX) ? NULL \
+				: realloc((p), (n) ? (n) : 1))
 
 #endif	/* PYMALLOC_DEBUG */
 
@@ -80,24 +84,31 @@ PyAPI_FUNC(void) PyMem_Free(void *);
  * Type-oriented memory interface
  * ==============================
  *
- * These are carried along for historical reasons.  There's rarely a good
- * reason to use them anymore (you can just as easily do the multiply and
- * cast yourself).
+ * Allocate memory for n objects of the given type.  Returns a new pointer
+ * or NULL if the request was too large or memory allocation failed.  Use
+ * these macros rather than doing the multiplication yourself so that proper
+ * overflow checking is always done.
  */
 
 #define PyMem_New(type, n) \
-  ( assert((n) <= PY_SIZE_MAX / sizeof(type)) , \
+  ( ((n) > INT_MAX / sizeof(type)) ? NULL : \
 	( (type *) PyMem_Malloc((n) * sizeof(type)) ) )
 #define PyMem_NEW(type, n) \
-  ( assert((n) <= PY_SIZE_MAX / sizeof(type)) , \
+  ( ((n) > INT_MAX / sizeof(type)) ? NULL : \
 	( (type *) PyMem_MALLOC((n) * sizeof(type)) ) )
 
+/*
+ * The value of (p) is always clobbered by this macro regardless of success.
+ * The caller MUST check if (p) is NULL afterwards and deal with the memory
+ * error if so.  This means the original value of (p) MUST be saved for the
+ * caller's memory error handler to not lose track of it.
+ */
 #define PyMem_Resize(p, type, n) \
-  ( assert((n) <= PY_SIZE_MAX / sizeof(type)) , \
-	( (p) = (type *) PyMem_Realloc((p), (n) * sizeof(type)) ) )
+  ( (p) = ((n) > INT_MAX / sizeof(type)) ? NULL : \
+	(type *) PyMem_Realloc((p), (n) * sizeof(type)) )
 #define PyMem_RESIZE(p, type, n) \
-  ( assert((n) <= PY_SIZE_MAX / sizeof(type)) , \
-	( (p) = (type *) PyMem_REALLOC((p), (n) * sizeof(type)) ) )
+  ( (p) = ((n) > INT_MAX / sizeof(type)) ? NULL : \
+	(type *) PyMem_REALLOC((p), (n) * sizeof(type)) )
 
 /* In order to avoid breaking old code mixing PyObject_{New, NEW} with
    PyMem_{Del, DEL} and PyMem_{Free, FREE}, the PyMem "release memory"
Index: Python-2.4.4/Objects/obmalloc.c
===================================================================
--- Python-2.4.4.orig/Objects/obmalloc.c
+++ Python-2.4.4/Objects/obmalloc.c
@@ -585,6 +585,15 @@ PyObject_Malloc(size_t nbytes)
 	uint size;
 
 	/*
+	 * Limit ourselves to INT_MAX bytes to prevent security holes.
+	 * Most python internals blindly use a signed Py_ssize_t to track
+	 * things without checking for overflows or negatives.
+	 * As size_t is unsigned, checking for nbytes < 0 is not required.
+	 */
+	if (nbytes > INT_MAX)
+		return NULL;
+
+	/*
 	 * This implicitly redirects malloc(0).
 	 */
 	if ((nbytes - 1) < SMALL_REQUEST_THRESHOLD) {
@@ -814,6 +823,15 @@ PyObject_Realloc(void *p, size_t nbytes)
 	if (p == NULL)
 		return PyObject_Malloc(nbytes);
 
+	/*
+	 * Limit ourselves to INT_MAX bytes to prevent security holes.
+	 * Most python internals blindly use a signed Py_ssize_t to track
+	 * things without checking for overflows or negatives.
+	 * As size_t is unsigned, checking for nbytes < 0 is not required.
+	 */
+	if (nbytes > INT_MAX)
+		return NULL;
+
 	pool = POOL_ADDR(p);
 	if (Py_ADDRESS_IN_RANGE(p, pool)) {
 		/* We're in charge of this block */
Index: Python-2.4.4/Misc/NEWS
===================================================================
--- Python-2.4.4.orig/Misc/NEWS
+++ Python-2.4.4/Misc/NEWS
@@ -23,6 +23,13 @@ What's New in Python 2.4.4c1?
 Core and builtins
 -----------------
 
+- Issue #2620: Overflow checking when allocating or reallocating memory
+  was not always being done properly in some python types and extension
+  modules.  PyMem_MALLOC, PyMem_REALLOC, PyMem_NEW and PyMem_RESIZE have
+  all been updated to perform better checks and places in the code that
+  would previously leak memory on the error path when such an allocation
+  failed have been fixed.
+
 - Added checks for integer overflows, contributed by Google. Some are
   only available if asserts are left in the code, in cases where they
   can't be triggered from Python code.
Index: Python-2.4.4/Modules/almodule.c
===================================================================
--- Python-2.4.4.orig/Modules/almodule.c
+++ Python-2.4.4/Modules/almodule.c
@@ -1633,9 +1633,11 @@ al_QueryValues(PyObject *self, PyObject 
 	if (nvals < 0)
 		goto cleanup;
 	if (nvals > setsize) {
+		ALvalue *old_return_set = return_set;
 		setsize = nvals;
 		PyMem_RESIZE(return_set, ALvalue, setsize);
 		if (return_set == NULL) {
+			return_set = old_return_set;
 			PyErr_NoMemory();
 			goto cleanup;
 		}
Index: Python-2.4.4/Modules/arraymodule.c
===================================================================
--- Python-2.4.4.orig/Modules/arraymodule.c
+++ Python-2.4.4/Modules/arraymodule.c
@@ -814,6 +814,7 @@ static int
 array_do_extend(arrayobject *self, PyObject *bb)
 {
 	int size;
+	char *old_item;
 
 	if (!array_Check(bb))
 		return array_iter_extend(self, bb);
@@ -829,10 +830,11 @@ array_do_extend(arrayobject *self, PyObj
 			return -1;
 	}
 	size = self->ob_size + b->ob_size;
+	old_item = self->ob_item;
         PyMem_RESIZE(self->ob_item, char, size*self->ob_descr->itemsize);
         if (self->ob_item == NULL) {
-                PyObject_Del(self);
-                PyErr_NoMemory();
+		self->ob_item = old_item;
+		PyErr_NoMemory();
 		return -1;
         }
 	memcpy(self->ob_item + self->ob_size*self->ob_descr->itemsize,
@@ -884,7 +886,7 @@ array_inplace_repeat(arrayobject *self, 
 			if (size > INT_MAX / n) {
 				return PyErr_NoMemory();
 			}
-			PyMem_Resize(items, char, n * size);
+			PyMem_RESIZE(items, char, n * size);
 			if (items == NULL)
 				return PyErr_NoMemory();
 			p = items;
Index: Python-2.4.4/Modules/selectmodule.c
===================================================================
--- Python-2.4.4.orig/Modules/selectmodule.c
+++ Python-2.4.4/Modules/selectmodule.c
@@ -342,10 +342,12 @@ update_ufd_array(pollObject *self)
 {
 	int i, pos;
 	PyObject *key, *value;
+        struct pollfd *old_ufds = self->ufds;
 
 	self->ufd_len = PyDict_Size(self->dict);
-	PyMem_Resize(self->ufds, struct pollfd, self->ufd_len);
+	PyMem_RESIZE(self->ufds, struct pollfd, self->ufd_len);
 	if (self->ufds == NULL) {
+                self->ufds = old_ufds;
 		PyErr_NoMemory();
 		return 0;
 	}